PHYSIOLOGICAL, MOLECULAR AND BIOCHEMICAL STUDIES ON EGYPTIAN MICROALGAE ISOLATES FOR POTENTIAL USE IN BIODIESEL PRODUCTION

Abstract

Blue-green algae (cyanobacteria) have all the potential to act as a platform for the development of fourth-generation biofuel. Nevertheless, the diversity and eco-physiology of blue-green algae in northern African countries and their biofuel production potential is still understudied. The aim of this thesis was screening eight isolates of blue-green algae belonging to genera of Anabaena (A. circinalis, A. fertilissima, A. sphaerica, A. variabilis, and A. sp.) and Nostoc (N. commune, N. muscorum, and N. sp.) for high lipid productivity, and to select the best isolate to further increase its lipid induction using different treatments. The results revealed that A. sphaerica was the superior isolate with good fatty acids profile and with the highest lipids productivity which was attributed to high specific growth rate and high lipid concentration. A. sphaerica was then subjected to different treatments including culture operation mode, media duplicity as well as different nutrition strategies in terms of nutrients supplementation or elimination (i.e. two stages mode of nutrition). All studied parameters of A. sphaerica were found to be best induced by NO3 or PO4 elimination in two stages mode of nutrition, as well as under 60M FeCl3 supplementation. The environmental adaptability of A. sphaerica for lipid production under single or/and combined salt (50, 75, and 100 mM NaCl) and mild heat stress (35 ºC) was evaluated, and it was found that lipids productivity was best induced under all studied NaCl concentrations, while the 35 ºC treatment slightly increased both lipid yield and lipids % of A. sphaerica. When NaCl was combined with 35 ºC, all parameters were increased, although to a lower degree than in a single factor. The combined effects of best studied treatments (+50 mM NaCl, -NO3, -P, +60 M FeCl3) were evaluated for lipids induction including double, triple as well as quadruple combinations. Generally, triple and quadruple combinations decreased most parameters, whereas –P and +60 M FeCl3 in a double combination was the only treatment that synergistically induced lipids as compared to single effect of each factor alone. Finally, identification of the A. sphaerica strain was based on molecular studies on the 16S rDNA sequence of A. sphaerica which was submitted to the NCBI GenBank database (accession No. MK271089) and the strain was named Anabaena sphaerica FSR1. Estimated biodiesel properties of Anabaena sphaerica FSR1 calculated from 5 previous treatments, i.e. +60 M FeCl3, –NO3, +50 mM NaCl, +Fe –P, and +Na+Fe–P were apparently found within the range of the biodiesel standards EN 14213 and EN 14214 (Europe), especially ASTM D6751–08 (United States). We recommend opting for the treatment that induces the highest lipid productivity to be more economically feasible, which was found to be the addition of 50 mM NaCl to the BG-110 media. Future studies involving this valuable strain are recommended to screen for useful bio products as well as assessing the success of its open air culturing.